Crystal-less Communications Device and Self-Calibrated Embedded Virtual Crystal Clock Generation Method

ABSTRACT

This invention discloses a crystal-less communication device and self-calibrated embedded virtual crystal clock generation method. In communication systems, the invention proposes a crystal-less scheme in the device for wireless or wired-line communications. The operation concepts are that the transmitter Device- 1  provides Device- 2  a reference signal, and Device- 2  takes this signal to generate a local signal with the similar frequency that has limited frequency error compared with the one from Device- 1 . This invention is done via the circuit-design methodology, so it can be implemented from any kinds of circuit implementation processes, especially the CMOS process. As a result, the hardware can be designed in the way of highly integration and extremely low cost. Also, this can largely change and improve existing communications design architecture, hardware cost, and hardware area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication device, moreparticularly to a crystal-less communication device and self-calibratedembedded virtual crystal clock generation method.

2. Description of the Prior Art

All kinds of wireless communications in today's electronic products, forexample mobile phones, Wireless Metropolitan Area Networks (WMAN),Wireless Local Area Network (WLAN), Satellite Positioning Systems (GPS),and Bluetooth, in addition to emphasize their ease of use and size ofappearance, the performance of those cannot be ignored from the focus ofresearch and development. There is no doubt that the base technologiesin transmit and receive component are their key functions and play animportance key role successfully.

Existing communications system designs require a crystal to generatereference frequency for the whole system for correct frequency andtiming synchronizations in transmitter and receiver. However, the areaoccupied and the cost from a crystal is extremely large, as shown inFIG. 1. When the communication devices 10 and 20 establish wirelesscommunication, the transmitter and receiver ends need to ensure that thetiming and frequency in both communication devices 10 and 20 aresynchronized. In order to achieve this objective, there must be areference clock immune from the external environment changes, likevariances in the manufacturing process, operating voltage andtemperature. In order to get a reference frequency away from externalenvironment changes, the current wireless transceivers are using anoscillator 30 as a reference frequency. The oscillator 30 with the basicphysical characteristics can be a stable frequency source. However, theoscillator 30 share its considerable size, also its hardware price andmounting procedure are very expensive.

Nowadays, existing crystal-less related technologies only achievelimited context about the oscillator. Those technologies can control thefrequency error generated by oscillator in a certain range, but thisrange is only the processor related application can accept.

In the U.S. Pat. No. 6,219,797, A microprocessor has an ability tooperate via an external crystal oscillator or be switched to operate ina low power mode via an internal ring oscillator. This patent has thefrequency error |Δf|≧2.5% which is 625 times bigger than thecommunications system can tolerate range (40 ppm), so it does not applyto communications devices.

In the U.S. Pat. No. 6,219,797, an integrated crystal-less devicegenerates an output signal with the frequency of the output signaldependent at least in part on a resistive element. The providedcircuitry for providing compensation for the temperature coefficient ofresistive element, the circuitry includes a bandgap reference and aresistive network. This patent has the frequency error |Δf|≧2.5% whichis 625 times bigger than the communications system can tolerate range(40 ppm), so it also does not apply to communications devices.

Krishnakumar Sundaresan, et. Al., (IEEE J. Solid-State Circuits, vol.41, no. 2, pp. 433-442) reports on the design and characterization of aprocess, temperature and supply compensation technique for a 7-MHz clockoscillator in a 0.25/spl mu/m, two-poly five-metal (2P5M) CMOS process.The paper has the frequency error |Δf|≧2.5% which is 625 times biggerthan the communications system can tolerate range (40 ppm), so it isimpossible to apply to communications devices.

In WBAN applications, we have ultra-low power requirements for WSNsbecause of the portable and long period body health monitorconsiderations. Although crystal-less based system can reduce largepower consumption, it suffers a significant clock mismatch between theCPN and WSNs that could damage the system performance because of SCO andCFO. This clock mismatch is resulted from the PVT issue when the ringoscillator is used. The existing crystal-less oscillator that theprogrammers are designed in a manner that in the absence of quartzcrystal as a reference frequency support, how to overcome the externalenvironment parameters drift of the oscillator frequency error. Andthese were related to the design of the microprocessor-related systemsand applications.

However, in a wired or wireless communication systems, to send andreceive signals successfully, the frequency of error that transceiverscan tolerate at both ends is very low, so only to control the error ofoscillator still cannot achieve applications' communication. In order todeal with the clock mismatch issue between the CPN and WSNs, we need toestimate the value of the mismatch and then “tune” or “adjust” the ringoscillator toward the correct clock period. Therefore, to find othersolutions in communication systems in the realization of a crystal-lesstechnology must have another thinking.

SUMMARY OF THE INVENTION

To solve the above-mentioned problem, the present invention provides acrystal-less communication device for wireless or wired-linecommunications, which adopts an embedded virtual crystal to makecommunication device operative without a physical crystal. The embeddedvirtual crystal can be implemented from any kinds of circuitimplementation processes, especially the CMOS process. As a result, thehardware can be designed in the way of highly integration and extremelylow cost. Also, this can largely change and improve existingcommunications design architecture, hardware cost, and hardware area.

To solve the above-mentioned problem, the present invention provides aself-calibrated embedded virtual crystal clock generation method in acommunication device, the self-calibrated and synchronization processwill be finished before the reference signal stops. Afterself-calibrated process is finished, the embedded virtual crystal canprovide precise clock signals to other connected circuits in thecrystal-less communication device.

To achieve the above-mentioned objective, one embodiment of the presentinvention provides a crystal-less communication device, including acommunication device receiving signals transmitted from a remotecommunication device and processing the signals with output pulses froman embedded virtual crystal to generate signals for the communicationdevice, wherein the signals are similar to oscillator's signals and makecommunication device operative.

To achieve the above-mentioned objective, another embodiment of thepresent invention provides a crystal-less communication device,including: a frequency differentiation unit receiving a first signaltransmitted from a remote communication device and processing the firstsignal to generate a differential signal; an embedded virtual crystaloscillator coupled to the frequency differentiation unit and receivingthe differential signal for calibration, and generating an output pulse;and a synthesizer coupled to the frequency differentiation unit and theembedded virtual crystal oscillator for receiving and processing theoutput pulse, and generating a second signal to the frequencydifferentiation unit.

To achieve the above-mentioned objective, another embodiment of thepresent invention provides a self-calibrated embedded virtual crystalclock generation method in a communication device, including: receivinga reference signal; comparing the reference signal and an output pulsefrom an embedded virtual crystal oscillator in the communication device;detecting the differential value between the reference signal and theoutput pulse; calculating the differential value to generate a numericerror; and renewing the output pulse in the embedded virtual crystaloscillator by using the numeric error.

Other advantages of the present invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings, which are set forth by way of illustration and example, tocertainly embody the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the accompanying advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a conventional communication devicewith a crystal oscillator in a communication system;

FIG. 2 is a schematic diagram illustrating a crystal-less communicationdevice according to one embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating a detail description for thecrystal-less communication device in FIG. 2;

FIG. 4 is a graph illustrating initial mismatch and remaining frequencyerror after frequency detection with various FFT lengths according toone embodiment of the present invention; and

FIG. 5 is a flowchart of a self-calibrated embedded virtual crystalclock generation method in a crystal-less communication device accordingto one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed explanation of the present invention is described asfollowing. The described preferred embodiments are presented forpurposes of illustrations and description, and they are not intended tolimit the scope of the present invention.

In communications systems, we have low area or cost requirements. Tomeet these requirements, the present invention proposes a crystal-lessscheme in the device for wireless or wired-line communications.

A crystal-less communication device receives signals transmitted from aremote communication device and processes the signals with output pulsesfrom an embedded virtual crystal to generate stable frequency signalsfor the crystal-less communication device, wherein the stable frequencysignals are similar to oscillator's signals and make communicationdevice operative. The crystal-less communication device and the remotecommunication device communicate in a wire-line or wirelesscommunication system.

The present invention discloses the concept of a ‘Virtual Crystal’ toprevent from the use of a real physical crystal. This is achieved viathe circuit-design methodology to realize this required referencefrequency. FIG. 2 is a schematic diagram illustrating a crystal-lesscommunication device according to one embodiment of the presentinvention. A remote communication device 60 transmits a reference signalto the crystal-less communication device 40, in which a frequencydifferentiation unit 43 receives the reference signal and processes itto generate a differential signal to an embedded virtual crystal 50. Alocal clock generator (not shown) in the embedded virtual crystal 50couples to a synthesizer 45, which coupled to the frequencydifferentiation unit 43, to provide output pulses for it. The frequencydifferentiation unit 43 receives the reference signal and the outputsignal from the synthesizer 45 to generate a differential signal becauseof mismatch between two frequencies. If the differential signal has itserror within the range that the base band system can tolerate, then thedifferential signal is sent to the signal decoding modulator 44;otherwise the embedded virtual crystal 50 will receive and process itfor frequency mismatch recovery.

A filter 42 is coupled to the input end of the frequency differentiationunit 43 to remove noise signal components in the reference signal.

When the reference signal from the remote communication device 40 haserror, the differential signal from the frequency differentiation unit43 will have frequency error or phase error specifying theircharacteristics. So the present invention uses the embedded virtualcrystal 50 as an oscillator, which receives the differential signal andthe output pulse from the local clock generator to output an oscillatingfrequency for clock mismatch recovery. The synthesizer 45 adjusts theoutput pulse in a receivable range to the frequency differentiation unit43. At last step, the signal decoding modulator 44 coupled to thefrequency differentiation unit 43 receives the differential signal,wherein the differential signal is within a fixed margin of error;otherwise the signal decoding modulator 44 will not be activated todecode the output signal from the frequency differentiation unit 43.

FIG. 3 is a schematic diagram illustrating a detail description for thecrystal-less communication device in FIG. 2. The filter 51 is coupled tooutput end of the frequency differentiation unit 43 to remove noisesignal components in output signals. A differential detector 52 coupledto the frequency differentiation unit 43 for receiving the differentialsignals can detect differences between the frequency of the remotecommunication device 60 and crystal-less communication device 40 andgenerate a differential feature. A differential calculator 54 is coupledto the differential detector 52 to receive the differential feature togenerate a frequency error. Then the frequency error is sent to a localclock generator 53 for adjustment to provide an output pulse to thesynthesizer 45, which receives and processes the output pulse andgenerate a signal to the frequency differentiation unit 43. If theoutput pulse has its error range under the circumstance that thefrequency differentiation unit 43 can make down-conversion of the signalfrom the remote communication device, the signal decoding modulator 44will begin decoding the signal to generate data signal. The embeddedvirtual crystal 50 disclosed by the present invention can be implementedin a circuit design to simulate all functions of a crystal oscillatordoing in the circuit. In some embodiments the embedded virtual crystal50 embodied in communications chips will has smaller size and lower costfor the crystal-less communication device.

Referring to FIG. 3, the present invention can be used in wirelesscommunication system. The remote communication device 60 transmits areference signal with precise 1.4 GHz frequency to the crystal-lesscommunication device 40 as a reference signal to “tune” or “adjust” theinternal clock frequency. As the crystal-less communication device 40turns on, the local clock generator 53 generates a 35 MHz f_(baseband)clock pulse, which has a clock mismatch (ε) controlled within absolutevalue of 2.5%. The synthesizer 45 generates 40 times of 1.4 GHzfrequency f_(out), which has same clock mismatch (|ε|≦2.5%) as localclock generator 53 does.

The low pass filter 42 and the frequency differentiation unit 43 makethe reference signal down conversion to R_(before LPF) as the equation(1).

$\begin{matrix}\begin{matrix}{{R_{{before}\; {LPF}}(t)} = {{synthesize}\mspace{14mu} {r\_ out}*{reference\_ signal}}} \\{= {{\cos \left\lbrack {2\; {\pi \cdot 1.4}\; {G\left( {1 + ɛ} \right)}} \right\rbrack}{t \cdot {\cos \left( {2\; {\pi \cdot 1.4}\; G} \right)}}t}} \\{= {{\frac{1}{2}{\cos \left( {2\; {\pi \cdot 1.4}\; {G \cdot ɛ}} \right)}t} +}} \\{{\frac{1}{2}{\cos \left\lbrack {2\; {\pi \cdot 1.4}\; {G \cdot \left( {2 + ɛ} \right)}} \right\rbrack}t}}\end{matrix} & (1)\end{matrix}$

As ε=2.5%, a low pass filter 51 with baseband 35 MHz frequency filtersoff high frequency in equation (1), the output of the low pass filter 51is expressed as equation (2)

$\begin{matrix}{{R_{afterLPF}(t)} = {\frac{1}{2}{\cos \left( {2\; {\pi \cdot 1.4}\; {G \cdot ɛ}} \right)}t}} & (2)\end{matrix}$

It shows the maximum of R_(after LPF) is 35 MHz if ε=2.5%, meaning thefrequency of R_(after LPF) can be calculated to obtain clock mismatch(ε). The differential detector 52 is designed to detect the frequencybetween 56 kHz and 35 MHz. The frequency that the differential detector52 detects will provide the local clock generator 53 to adjust theoutput frequency. The frequency for the differential detector 52 islower than 56 kHz; clock mismatch (ε) is below the value 40 ppmspecified by the system.

Accordingly the overall performance of embedded virtual crystal 50 actsas a virtual crystal to recovery reference clock within the margin oferror required by the system.

In one embodiment, the differential detector 52 can be realized by usingan ADC circuit and a FFT circuit. As the differential detector 52receives R_(after LPF), the ADC circuit samples R_(after LPF) to getdigital signal that is transformed to the FFT circuit. The output of FFTcircuit is a signal spread in frequency domain, which presents thefrequency components in R_(after LPF), thus the frequency detection isdone. Referring the FIG. 4 is a graph illustrating initial mismatch andremaining frequency error after frequency detection with various FFTlengths. The differential detector 52 with FFT Length=4096 above (L5,L6, L7, L8) is capable of detecting the frequency of R_(ater LPF) andcontrol the frequency error below 40 ppm. Meaning the frequency error of2.5% is lower than 40 ppm.

According to the mention above, the present invention disclosesoperation concepts that the remote communication device (transmitter)provides crystal-less communication device (receiver) a referencesignal, and crystal-less communication device processes this signal togenerate a corresponding reference frequency, which matches the one fromthe remote communication Device. The reference signal is a crystal-likesignal to provide the crystal-less communication device a operationalfrequency.

Referring FIG. 5 is a flowchart of a self-calibrated embedded virtualcrystal clock generation method in a crystal-less communication deviceaccording to one embodiment of the present invention. The methodoperating in communication system includes following steps: the step S31receiving a reference signal, a crystal-lass communication devicereceives a reference signal from a remote communication device; the stepS32 filtering the reference signal, a filter removes unwanted signal toextract the reference signal; step S63 comparing between the localsignal and the reference signal, an output pulse from an embeddedvirtual crystal in the communication device are compared with thereference signal; step S64 detecting the differential value between thereference signal and the output pulse; step S65 calculating thedifferential value to generate a numeric error; step S66 renewing theoutput pulse in the embedded virtual crystal oscillator by using thenumeric error; step S67 is the mismatch frequency tolerated? Afterrenewing the output pulse in the embedded virtual crystal oscillator, ifthe output pulse's error is within a fix range then begin step S68 toencode the coming signal, otherwise goes to step S63, S64, S65, S66 tocontinue generating the next numeric error until the output pulsematches the frequency of the communication system. The output pulseafter renewing step is a precise clock signal.

The numeric error is a frequency error or phase error.

In the self-calibrated embedded virtual crystal clock generation method,the self-calibrated and synchronization process will be finished beforethe reference signal stops. After self-calibrated process is finished,the embedded virtual crystal can provide precise clock signals to otherconnected circuits in the crystal-less communication device.

Therefore, in the condition of non-use of physical oscillator, thepresent invention discloses the concept of embedded virtual crystal, theuse of the circuit design similar to the way of oscillator's frequencyto be a reference clock (shown in FIG. 2 and FIG. 3). The operationconcepts are that the transmitter provides the receiver a referencesignal, and receiver takes this reference signal to generate acorresponding reference frequency, which matches the one from thetransmitter. As a result, the concept of a ‘Virtual Crystal’ preventsfrom the use of a real physical crystal. This is achieved via thecircuit-design methodology to realize this required reference frequency,as shown in FIG. 2. By current CMOS process, the present invention maybe integrated in one communication ship with other circuits toaccomplish small size and low cost purpose. This changes current circuitdesign, which uses an isolate crystal, to bright an architectureimprovement.

Those skilled in the art can realize that the teachings of the presentinvention as described hereinabove provides circuitry that comprehendsabove. In order to maintain a successful communication link between thetransceivers, the frequency error is controlled in the ±20 ppm. Thus thepresent invention in the non-use of crystal using system correctionmethod coupled with hardware approach, has the ability to control thecommunications device to achieve the required frequency accuracy.Regardless of how much frequency mismatch the transceivers initiallyhave at both ends, the invention of the method will convergence thefrequency error to the accuracy, to achieve further success of thecommunication.

Furthermore, this invention is done via the circuit-design methodology,so it can be implemented from any kinds of circuit implementationprocesses, especially the CMOS process. As a result, the hardware can bedesigned in the way of highly integration and extremely low cost. Also,this can largely change and improve existing communications designarchitecture, hardware cost, and hardware area.

While the invention is susceptible to various modifications andalternative forms, a specific example thereof has been shown in thedrawings and is herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formdisclosed, but to the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the appended claims.

1. A crystal-less communication device, comprising: a communicationdevice receiving signals transmitted from a remote communication deviceand processing the signals with output pulses from an embedded virtualcrystal to generate signals for the communication device, wherein thesignals are similar to oscillator's signals and make communicationdevice operative.
 2. The crystal-less communication device as claimed inclaim 1, wherein the crystal-less communication device and the remotecommunication device communicate in a wire-line or wirelesscommunication system.
 3. A crystal-less communication device,comprising: a frequency differentiation unit receiving a first signaltransmitted from a remote communication device and processing the firstsignal to generate a differential signal; an embedded virtual crystalcoupled to the frequency differentiation unit and receiving thedifferential signal for calibration, and generating an output pulse; asynthesizer coupled to the frequency differentiation unit and theembedded virtual crystal oscillator for receiving and processing theoutput pulse, and generating a second signal to the frequencydifferentiation unit.
 4. The crystal-less communication device asclaimed in claim 3, further comprising a first filter coupled to theinput end of the frequency differentiation unit to remove noise signalcomponents in the first signal.
 5. The crystal-less communication deviceas claimed in claim 3, further comprising a signal decoding modulatorcoupled to the frequency differentiation unit to receive thedifferential signal, wherein the differential signal is within a fixedmargin of error.
 6. The crystal-less communication device as claimed inclaim 3, wherein the embedded virtual crystal oscillator furthercomprising: a local clock generator for providing a pulse signal for thecrystal-less communication device; a differential detector coupled tothe frequency differentiation unit for receiving the differentialsignals to generate a differential feature; and a differentialcalculator coupled to the differential detector for receiving thedifferential feature to generate an frequency error.
 7. The crystal-lesscommunication device as claimed in claim 6, further comprising a secondfilter coupled to output end of the frequency differentiation unit toremove noise signal components in the differential signal.
 8. Aself-calibrated embedded virtual crystal clock generation method in acommunication device, comprising: receiving a reference signal;comparing the reference signal and an output pulse from an embeddedvirtual crystal oscillator in the communication device; detecting thedifferential value between the reference signal and the output pulse;calculating the differential value to generate a numeric error; andrenewing the output pulse in the embedded virtual crystal oscillator byusing the numeric error.
 9. The self-calibrated embedded virtual crystalclock generation method in a communication device as claimed in claim 8,wherein the numeric error is a frequency error.
 10. The self-calibratedembedded virtual crystal clock generation method in a communicationdevice as claimed in claim 8, wherein the numeric error is a phaseerror.
 11. The self-calibrated embedded virtual crystal clock generationmethod in a communication device as claimed in claim 8, wherein thereference signal is transmitted from a remote communication devicewithin a communication system.
 12. The self-calibrated embedded virtualcrystal clock generation method in a communication device as claimed inclaim 8, further comprising removing noise signal components in thereference signal.
 13. The self-calibrated embedded virtual crystal clockgeneration method in a communication device as claimed in claim 8,further comprising after renewing the output pulse in the embeddedvirtual crystal oscillator, if the output pulse's error is within a fixrange then begin encoding, otherwise continue generating the nextnumeric error.
 14. The self-calibrated embedded virtual crystal clockgeneration method in a communication device as claimed in claim 8,wherein the output pulse after renewing step is a precise clock signal.15. The self-calibrated embedded virtual crystal clock generation methodin a communication device as claimed in claim 8, further comprisingbefore the reference signal stops, finishing the self-calibrated andsynchronization process in the embedded virtual crystal oscillator, 16.The self-calibrated embedded virtual crystal clock generation method ina communication device as claimed in claim 8, further comprising afterself-calibrated process in the embedded virtual crystal oscillator isfinished, the embedded virtual crystal oscillator providing preciseclock signals to circuits in the communication device.